First-Principle Investigations of (Ti1-xVx)(2)FeGa.lloys. A Study on Structural, Magnetic, Electronic, and Elastic Properties

The structural, magnetic, electronic and elastic properties of ternary and quaternary (Ti1-xVx)(2)FeGa alloys with inverse-Heusler (XA) structure were investigated at x = 0, 0.25, 0.50, 0.75, and 1. The crystal structures of (Ti1 - xVx)(2)FeGa compounds are cubic (space group: F (3) over barm) with Hg2CuTi prototype for x = 0 and 1. At x = 0.5 the structure is also cubic (space group: F (3) over barm) with LiMgPdSn protype, while it is tetragonal (space group: P m2) at x = 0.25 and 0.75. Calculated optimized lattice parameters (a and c), bulk modulus (B), and elastic constants (C-ij) are consistent with the available data in the literature. Total and partial magnetic moments of (Ti1 - xVx)(2)FeGa alloys were obtained. An increase in the total magnetic moment values were observed upon addition of V to the Ti2FeGa alloy. From spin polarized band calculations, Ti2FeGa, (Ti0.75V0.25)(2)FeGa, TiVFeGa, and V2FeGa have a minority-spin energy gap of 0.65, 0.38, 0.83, and 0.64 eV, respectively, and they are guessed as half-metallic ferromagnets. According to the results of second-order elastic constants, these compounds met the Born mechanical stability criteria. In addition, according to Pugh criteria, it was found that they have a ductile structure and show anisotropic behavior

An experimental and theoretical study of molecular structure and vibrational spectra of 3-and 4-pyridineboronic acid molecules by density functional theory calculations

WOS: 000257573000029PubMed ID: 17933583The experimental and theoretical vibrational spectra of 3- and 4-pyridineboronic acids (abbreviated as p3 and p4) were studied. The Fourier transform Raman and Fourier transform infrared spectra of p3 and p4 molecules were recorded in the solid phase. The structural and spectroscopic analysis of the p3 and p4 acids were made by using density functional harmonic calculations. Both p3 and p4 only one form was most stable using B3LYP level with the 6-31G(d), 6-31G(d,p), 6-311G(d), 6-311G(d,p) and 6-311++G(d,p) basis sets. Selected experimental bands were assigned based on the scaled theoretical wavenumbers. Finally, geometric parameters, infrared and Raman bands and intensities were compared with experimental data of the molecules. (C) 2007 Elsevier B.V. All rights reserved

Feedback Delay Effects on Physical Layer Security in A Dual-Hop Half/Full-Duplex Bi-directional Wireless Relaying Networks

This paper investigates the feedback delay effects on physical layer security. The investigation considers a dual-hop single amplify-and-forward based untrustworthy half/full-duplex two-way relay with a finite number of friendly jammers in the system model. According to the Monte-Carlo simulation results, the feedback delay degrades the system secrecy achievable rate and causes system coding gain losses in high signal-to-noise regimes. Results also show that if the number of friendly jammers in the system model increases then system secrecy achievable rate tends to degrade and causes system coding gain losses. Results also show that better system secrecy achievable rate can be achieved when the relay terminal operates in full-duplex mode

Ab-initio study of the structural, electronic, elastic and vibrational properties of HfX (X = Rh, Ru and Tc)

WOS: 000396759100004The structural, elastic, electronic and phonon properties of HfX (X = Rh, Ru and Tc) in the caesium-chloride phase have been investigated using the density functional theory within the generalized gradient approximation. The optimized lattice constant (a(0)), bulk modulus (B) and the elastic constants (C-ij) are evaluated. The results are in a good agreement with the available experimental and theoretical data in the literature. Electronic band structures and densities of states have been derived for these compounds. The present band structure calculations indicate that the phases of caesium-chloride HfX (X = Rh, Ru and Tc) compounds are metals. Phonon dispersion curves and their corresponding total and projected density of states have been obtained using the direct method. The phonon spectra suggest that these compounds are dynamically stable in the caesium-chloride phase.AhiEvran University Research Project UnitAhi Evran University [PYO-EGF.4001.14.003, FEF.A3.16.022, PYO-FEN.4001.14.018]This work was supported by the AhiEvran University Research Project Unit [project number PYO-EGF.4001.14.003], [project number FEF.A3.16.022]; and [project number PYO-FEN.4001.14.018]

Opportunistic Source-Pair Selection (OSPS) Method for Multiuser Bi-directional Wireless Relaying Networks

This paper investigates the opportunistic source-pair selection (OSPS) strategy for the co-channel interference challenge in multiuser amplify-and-forward based bi-directional wireless relaying networks. The method relies upon selection of the appropriate source-pair node among N available source-pair nodes based on each source pair's maximum sum capacity. According to the simulation results, the OSPS strategy, besides achieving the near optimal solution for the co-channel interference challenge, and if the number of the user pair increases, also achieves multiuser diversity order by selecting the maximum sum-capacity user-pair in each time slot

An examination of the structural, electronic, elastic, vibrational and thermodynamic properties of Ru2YGa (Y = Sc, Ti and V) Heusler alloys

WOS: 000442353500041The structural, electronic, elastic, vibrational and thermodynamic properties of the Ru2YGa (Y = Sc, Ti and V) Heusler alloys in L2(1) type cubic structure have been analyzed systematically using first principles density functional theory (DFT) together with the Generalized Gradient Approximation (GGA) method. The values of calculated lattice constant (a(0)), elastic constants (Cij), Bulk modulus (B), Shear modulus (G), ratios of B/G, Young's modulus (E) and Poisson ratio (v) are in good agreement with the available theoretical and experimental results. The electronic band structures, corresponding total and partial density of states have also been obtained. The calculated band structures demonstrate that Ru2YGa (Y = Sc, Ti and V) alloys are metallic. The phonon dispersion curves, total and partial density of states of these alloys have been computed for the first time by adopting the direct method. It is considered that all alloys are dynamically stable in L2(1) structure

Opportunistic source-pair selection method with imperfect channel state information for multiuser bi-directional relaying networks

This study investigates the impact of imperfect channel state information that is caused by feedback delay with time-variant channels and also by channel estimation errors with an opportunistic source-pair selection strategy. The investigation considers multi-user bi-directional wireless relaying networks. The opportunistic source-pair selection strategy selects the appropriate source-pair node among N available nodes. The selection strategy is based on each source pair's maximum sum-rate in each time slot. According to analytical, asymptotic, and Monte-Carlo simulation results, the opportunistic source-pair selection strategy, besides achieving a near-optimal solution for inter-cell interference that is caused by other user-pairs in the system model, also achieves diversity order in high signal-to-noise regimes. Moreover, the opportunistic source-pair selection strategy outperforms the max-min-based selection strategy in such a system model. Results also show that feedback delay degrades the achievable diversity order from N to 0 while affecting coding gain. The results also show that the channel estimation error case does not affect the achievable diversity order, but it does affect the system coding gain in low-signal-to-noise regimes. Moreover, the channel estimation error effects upon system coding gain become negligible at high-signal-to-noise regimes

Molecular structure and vibrational spectra of 2-and 5-methylbenzimidazole molecules by density functional theory

WOS: 000278299800002PubMed ID: 20395166The FT-IR and FT-Raman spectra of 2-methylbenzimidazole (2-MB) and 5-methylbenzimidazole (5-MB) molecules have been recorded between 400-4000 cm(-1) and 50-3500 cm(-1) region, respectively. The molecular geometry and vibrational frequencies of 2- and 5-MB molecules in the ground state have been calculated by using the density functional methods (B3LYP) with 6-311++G(d,p) and 6-31G(d,p) as basis sets. The total energy distributions (TEDs) for the normal modes were computed for the minimum energy structure of the molecules. Comparison of the observed fundamental vibrational frequencies of 2- and 5-MB molecules with calculated results by density functional B3LYP approach will give better result for our studied molecular vibrational problem. (C) 2010 Elsevier B.V. All rights reserved.Gazi UniversityGazi University [30/2005-01]This work was supported by the Research Fund of the Gazi University Project Numbers: 30/2005-01. We wish to thank the central laboratory of METU for Raman spectra of molecule and Gazi University Art and Science Faculty, Department of Chemistry for Infrared spectra of molecule. The visit of Dr. N. Sundaraganesan to Ahi Evran University was facilitated by the Scientific and Technical Research Council of Turkey (TUBITAK) BIDEB-2221

Ab-initio study of the structural, electronic, elastic and vibrational properties of the intermetallic Pd3V and Pt3V alloys in the L1(2) phase

WOS: 000339957700024Pseudopotential plane-wave method based on density functional theory within the generalized gradient approximation for the exchange-correlation potential has been applied to study the structural, electronic, elastic and vibrational properties of the binary intermetallic Pd3V and Pt3V in the L1(2) phase. The optimized lattice constant, bulk modulus and its pressure derivative, independent single-crystal elastic constants and elastic wave velocities in three different directions are evaluated and compared with the available experimental and theoretical data. The polycrystalline elastic parameters, hardness coefficient, elastic anisotropy, Debye temperature are estimated. The electronic band structure, electronic total and partial densities of states, and total magnetic moment of the Pd3V and Pt3V alloys are computed and analyzed in comparison with the existing theoretical and experimental findings. Phonon-dispersion curves and their corresponding total and projected densities of states were obtained for the first time using a linear-response in the framework of the density functional perturbation theory.Ahi Evran University Research Project UnitAhi Evran University [FBE-11-29]; Gazi University Research Project UnitGazi University [05/2012-62, 05/2012-63, 05/2012-07, 05/2012-08]This work was supported by the Ahi Evran University Research Project Unit under Project No FBE-11-29 and the Gazi University Research Project Unit under Project No 05/2012-62, 05/2012-63, 05/2012-07, 05/2012-08